The present invention relates to copper (Cu) and/or Cu alloy metallization in semiconductor devices, and to a method for manufacturing semiconductor devices with reliable, low resistance Cu or Cu alloy interconnects. The present invention is particularly applicable to manufacturing high speed integrated circuits having submicron design features and high conductivity interconnect structures.
The escalating demand for high density and performance impose severe requirements on semiconductor fabrication technology, particularly interconnection technology in terms of providing reliable low RxC (resistance x capacitance) interconnect patterns with higher electromigration resistance, wherein submicron vias, contacts and trenches have high aspect ratios. Conventional semiconductor devices comprise a semiconductor substrate, typically doped monocrystalline silicon, and a plurality of sequentially formed interlayer dielectrics and conductive patterns. An integrated circuit is formed containing a plurality of conductive patterns comprising conductive lines separated by interwiring spacings, and a plurality of interconnect lines, such as bus lines, bit lines, word lines and logic interconnect lines. Typically, the conductive patterns on different layers, i.e., upper and lower layers, are electrically connected by a conductive plug filling a via hole, while a conductive plug filling a contact hole establishes electrical contact with an active region on a semiconductor substrate, such as a source/drain region. Conductive lines are formed in trenches which typically extend substantially horizontal with respect to the semiconductor substrate. Semiconductor xe2x80x9cchipsxe2x80x9d comprising five or more levels of metallization are becoming more prevalent as device geometry""s shrink to submicron levels.
A conductive plug filling a via hole is typically formed by depositing an interlayer dielectric on a conductive layer comprising at least one conductive pattern, forming an opening through the interlayer dielectric by conventional photolithographic and etching techniques, and filling the opening with a conductive material, such as tungsten (W). Excess conductive material on the surface of the interlayer dielectric is typically removed by chemical mechanical polishing (CMP). One such method is known as damascene and basically involves forming an opening in the interlayer dielectric and filling the opening with a metal. Dual damascene techniques involve forming an opening comprising a lower contact or via hole section in communication with an upper trench section, which opening is filled with a conductive material, typically a metal, to simultaneously form a conductive plug in electrical contact with a conductive line.
High performance microprocessor applications require rapid speed of semiconductor circuitry. The control speed of semiconductor circuitry varies inversely with the resistance and capacitance of the interconnection pattern. As integrated circuits become more complex and feature sizes and spacings become smaller, the integrated circuit speed becomes less dependent upon the transistor itself and more dependent upon the interconnection pattern. Miniaturization demands long interconnects having small contacts and small cross-sections. As the length of metal interconnects increases and cross-sectional areas and distances between interconnects decrease, the RxC delay caused by the interconnect wiring increases. If the interconnection node is routed over a considerable distance, e.g., hundreds of microns or more as in submicron technologies, the interconnection capacitance limits the circuit node capacitance loading and, hence, the circuit speed. As design rules are reduced to about 0.12 micron and below, the rejection rate due to integrated circuit speed delays significantly reduces production throughput and increases manufacturing costs. Moreover, as line widths decrease electrical conductivity and electromigration resistance become increasingly important.
Cu and Cu alloys have received considerable attention as a candidate for replacing Al in interconnect metallizations. Cu is relatively inexpensive, easy to process, and has a lower resistively than Al. In addition, Cu has improved electrical properties vis-à-vis W, making Cu a desirable metal for use as a conductive plug as well as conductive wiring.
An approach to forming Cu plugs and wiring comprises the use of damascene structures employing CMP. However, due to Cu diffusion through interdielectric layer materials, such as silicon dioxide, Cu interconnect structures must be encapsulated by a diffusion barrier layer. Typical diffusion barrier metals include tantalum (Ta), tantalum nitride (TaN), titanium nitride (TiN), titanium (Ti), titanium-tungsten (TiW), tungsten (W), tungsten nitride (WN), Tixe2x80x94TiN, titanium silicon nitride (TiSiN), tungsten silicon nitride (WSiN), tantalum silicon nitride (TaSiN) and silicon nitride for encapsulating Cu. The use of such barrier materials to encapsulate Cu is not limited to the interface between Cu and the dielectric interlayer, but includes interfaces with other metals as well.
In implementing Cu metallization, particularly in damascene techniques wherein an opening is formed in a dielectric layer, particularly a dielectric layer having a low dielectric constant, e.g., a dielectric constant less than about 3.9, various reliability, electromigration and resistance issues are generated. Reliability issues stem, in part, from the use of Ta or TaN, the barrier layers of choice in Cu metallization. Ta has been found to lack adequate adhesion to various interlayer dielectric materials, particularly, interlayer dielectric materials having a low dielectric constant, such as a dielectric constant (k) less than about 3.9, particularly fluorine (F) -containing dielectric materials, such as F-containing oxides, e.g., F-containing silicon oxide derived from F-tetraethyl orthosilicate (F-TEOS). Lack of sufficient barrier layer adhesion to dielectric layers results in delamination with attendant reliability issues. TaN has been found to lack adequate adhesion to Cu and Cu alloys filling a damascene opening. Moreover, Ta and TaN are typically deposited by physical vapor deposition (PVD) techniques, such as ionized (I) PVD. The resulting layer of Ta is typically xcex2-phase Ta (xcex2-Ta) which exhibits a relatively high resistivity, e.g., about 200 to about 250 xcexcohm-cm. TaN is typically deposited with a nitrogen (N2) content of about 30 to about 55 at.%, and exhibits a resistivity in excess of 200 xcexcohm-cm.
The adhesion problems adversely impact electromigration resistance and device reliability, while the high resistivity of TaN and xcex2-Ta manifestly adversely impact circuit speed. Accordingly, there exists a need for reliable, low resistance interconnects, particularly Cu and Cu alloy interconnects formed in low dielectric constant materials, and for enabling methodology.
An advantage of the present invention is a method of manufacturing a semiconductor device having reliable, low resistance interconnects, such as Cu or Cu alloy interconnects, exhibiting improved electromigration resistance.
Additional advantages and other features of the present invention will be set forth in the description which follows and, in part, will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a method of manufacturing a semiconductor device, the method comprising: forming an opening in a dielectric layer; laser thermal annealing exposed surfaces of the dielectric layer in nitrogen (N2) and hydrogen (H2); and forming a composite barrier layer comprising tantalum (Ta) lining in the opening.
Embodiments include forming a dual damascene opening in a dielectric layer having a low dielectric constant (k) less than about 3.9, such as F-containing silicon oxide derived from F-TEOS, and impinging a pulsed laser light beam on exposed surfaces of the dielectric layer employing a N2 flow rate of about 200 to about 2,000 sccm and a H2 flow rate of about 200 to about 2,000 sccm, thereby forming a surface region depleted in F and enriched in N2. Ta is then deposited, as by IPVD, such that the deposited Ta reacts with N2 in the N2-enriched surface region forming a layer of graded tantalum nitride containing N2 in an amount decreasing in a direction away from the N2-enriched surface region. Upon continuing deposition, a layer of xcex1-Ta is formed on the graded tantalum nitride layer which serves as an adhesion layer between the xcex1-Ta and F-TEOS. The opening is then filed with Cu or Cu alloy.
Embodiments of the present invention further include single and dual damascene techniques comprising forming an opening in a dielectric layer or layers on a wafer, laser thermal annealing exposed surfaces of the dielectric layer or layers in N2 and H2, depositing Ta to form a composite diffusion barrier layer of graded tantalum nitride/xcex1-Ta lining the opening and on the dielectric layer(s), depositing a seedlayer, depositing the Cu or a Cu alloy layer on the seedlayer filling the opening and over the dielectric layer(s), removing any portion of the Cu or Cu alloy layer beyond the opening by CMP leaving an exposed surface and depositing a silicon nitride or silicon carbide capping or barrier layer.